1. Field of the Invention
The present invention relates to an improved carburetor, and more particularly to a carburetor having pivotally mounted plates, which define a variable venturi, and a fuel metering system coordinated with the pivotal positions of the plates, the improvement relating to an enrichment fuel system usable, for example, for metering fuel during starting and cold weather conditions, for metering fuel during relatively high engine power requirements, and to condition the carburetor for different types of fuel.
2. Description of the Prior Art
The prior art includes carburetors characterized by having a housing providing a rectangular mixing passage leading to an internal combustion engine and a fuel chamber at one side of the passage, by having a throttle at the downstream end of the passage, by having a fuel spray bar extended transversely across and centrally of the passage, and by having a pair of venturi plates pivoted for movement about axes parallel to the bar and individually adjacent to a pair of opposite walls of the passage, the plates having a closed position in which they extend from their respective axes toward each other and across the passage and an open position extended in the direction of air flow along the passage. In such prior art carburetors, the plates are moved toward the open position by air flow toward the engine, this movement being resiliently opposed and coordinated by elements linking the plates. These carburetors are further characterized by a fuel metering system which includes a valve operably connected to the plates so as to be progressively opened and closed as the plates move, respectively, toward their open and their closed positions.
Examples of such venturi plate carburetors are disclosed in the Kendig U.S. Pat. No. 3,752,451 and in U.S. Pat. No. 4,283,355 to Herd, Jr., et al. The carburetors disclosed in these patents are characterized by their adaptability without significant alteration to a wide range of engines and operating conditions, by providing an even fuel distribution at the exit from the mixing passage, and by providing a desired fuel to air ratio over a wide range of air flow. The carburetor of the latter patent is particularly effective in providing even fuel distribution and proper fuel/air ratio at low and medium air flow.
It nevertheless has been recognized as desirable further to increase the adaptability and flexibility of performance of such carburetors by adapting an individual carburetor for use, without significant disassembly or machine work, to conditions requiring greatly increased fuel flow to enrich the fuel/air mixture provided by the carburetor. One example of such a use is in starting and/or cold weather. Another example is in an engine for use in a racing automobile or the like where a rich mixture is used to provide increased power and where conventionally precise adjustments are required for varying atmospheric conditions. A further example is in racing where methanol fuel is used, the mass rate of flow with such fuel being approximately double that of gasoline. Since a racing engine may be used at different times with various fuels, a carburetor for a racing engine which has the advantages of prior art venturi plate carburetors and which is easily, economically, and completely convertible from one fuel to another in a few minutes is highly desirable. Another example is the need to provide, for maximum power, an enriched mixture to an internal combustion engine normally operated at a relatively lean mixture for economy, as is usually the case with vehicle engines for street use. A further example is the use of ethanol and gasoline mixtures in engines for street use where, although operation is possible without alterations to a carburetor intended for gasoline only, superior performance from the standpoints of cruising economy and maximum power is possible only by varying the fuel to air ratios under these two conditions from the relative such ratios provided by a carburetor intended for use with gasoline only.